Columnar Liquid Crystalline Phase Research Articles

Unsymmetrical and C3-Symmetrical Partially Fluorinated Hexaarylbenzenes: Effect of Terminal Alkoxy Chain Length on Photophysical and Thermophysical Behavior

Solution-state photoluminescence (PL) is affected by the electronic state; however, solid-state PL varies widely depending on the aggregated state. Although the synthesis and photophysical properties of unsymmetrical and C3-symmetrical hexaarylbenzenes (HABs) have been reported, the influence of their terminal alkoxy chains on their physical properties remains unclear. Therefore, we synthesized a series of unsymmetrical and C3-symmetrical partially fluorinated HABs with different alkoxy chains and investigated the effects of alkoxy chain length on the thermophysical and photophysical properties. While investigating phase transition behavior, the ethoxy-substituted unsymmetrical derivative revealed a columnar liquid-crystalline phase, whereas the other derivatives only exhibited a phase transition between crystalline and isotropic phases. While evaluating PL behavior, both the unsymmetrical and C3-symmetrical analogs exhibited relatively strong blue PL, independent of the alkoxy chain length. Through-space π-conjugation caused the PL spectra of C3-symmetrical derivatives to redshift compared to those of unsymmetrical derivatives. Partially fluorinated HABs exhibited relatively strong fluorescence, even in the crystalline state, depending on the alkoxy chain length, owing to the formation of various aggregated structures. Crystalline fluorinated HABs exhibited photochromism, resulting in the appearance of long-wavelength PL bands when exposed to ultraviolet (UV) irradiation, making them promising candidates for PL sensing materials for UV detection.

Supramolecular copolymerization of hydrophobic and hydrophilic monomers in liquid crystalline media.

In the case of covalent polymers, immiscible polymers can be integrated by covalently linking them together, but such a strategy is not possible in supramolecular polymers. Here we report the supramolecular copolymerization of two porphyrin-based monomers, C10P2H and TEGPCu with side chains bearing cyanobiphenyl (CB) groups at the ends of hydrophobic alkyl or hydrophilic tetraethylene glycol chains, respectively. These monomers undergo self-sorting supramolecular polymerization in highly diluted solutions ([monomer] = 3.4 × 10-9 mol% (2.0 × 10-8 mol L-1)) in nonpolar media due to the incompatibility of the side chains. Surprisingly, these monomers undergo supramolecular copolymerization under high concentration conditions ([monomer] = 7.7 mol%) in the medium of 4-cyano-4'-pentyloxybiphenyl (5OCB) to form a columnar liquid crystalline phase under thermodynamic conditions, where the individual columns are composed of supramolecular block copolymers. The combination of CB ends of both monomers and the 5OCB medium is essential for the two monomers to form an integrated structure in a condensed system without phase separation.

Two-Dimensional Supramolecular Polymerization of a Bis-Urea Macrocycle into a Brick-Like Hydrogen-Bonded Network.

We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl3 or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development.

Spider dragline silk fibres maintain rectangular columnar liquid crystalline phase

ABSTRACT The liquid crystalline phase of spider silk is thought to enable for the silk protein to be stored at high concentration in the gland without gelation, facilitating the instant fibre formation at the spinning duct. Nevertheless, it has never been revealed whether the liquid crystalline state of the silk protein maintains after the fibre formation. In this study, we conducted the X-ray liquid crystal structure analysis to reveal the details of molecular assemblies of the native spider silk proteins. Based on the wide- and small angle X-ray scattering data using the uniaxial bundle of spider draglines, the spider dragline silk fibres maintain a rectangular columnar liquid crystalline phase with a P21/a (p2gg) symmetry. The liquid crystalline state of the spider silk fibre is not nematic, cholesteric, nor hexagonal columnar, as previously proposed, but rectangularly packed columnar liquid crystal. The movable silk molecular chains along the long fibre axis in the rectangular columnar liquid crystalline structure help to explain the mechanical strength of the native spider dragline silk fibres. The results obtained in this study will contribute to understanding the biological basis underlying the silk fibre formation and will be useful to the biomimicry of spider silk fibres.

Densest-known packings and phase behavior of hard spherical capsids.

By mostly using Monte Carlo numerical simulation, this work investigates the densest-known packings and phase behavior of hard spherical capsids, i.e., hard infinitesimally thin spherical caps with a subtended angle larger than the straight angle. The infinitely degenerate densest-known packings are all characterized by hard spherical capsids that interlock and can be subdivided into three families. The first family includes crystalline packings that are constructed by suitably rotating and stacking layers of hexagonally arranged and suitably tilted hard spherical capsids; depending on the successive rotations, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. The second family includes crystalline packings that are characterized by rhombic motifs; they all become the face-centered cubic crystal in the hard-sphere limit. The third family includes crystalline packings that are constructed by suitably shifting and stacking layers in which hard spherical capsids are arranged in tightly packed, straight or zigzag, columns; depending on the successive shifts, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. In the plane number density vs subtended angle, the phase diagram of hard spherical capsids features a hexagonal columnar liquid-crystalline phase, toward the hard-hemispherical-cap limit, and a plastic-crystalline phase, toward the hard-sphere limit, in addition to the isotropic fluid phase and crystalline phases. On departing from the hard-sphere limit, the increasing propensity of hard spherical capsids to interlock progressively disfavors the plastic-crystalline phase while favoring auto-assemblage into mostly dimeric interlocks in the denser isotropic fluid phase so that a purely entropic isotropic-fluid-plastic-crystal-isotropic-fluid re-entrant sequence of phase transitions is observed in systems of hard spherical capsids with a subtended angle intermediate between the straight angle and the complete angle.

Liquid Crystalline Magneto-Optically Active Peralkylated Azacoronene.

Organic Faraday rotators have gained significant attention in recent years as a promising alternative to traditional inorganic magneto-optical (MO) materials as a result of their lower cost, superior mechanical properties, and potential for large-scale deployment. This interest is peaked by the fact that a number of high symmetry, rigid, strongly optically absorbing organic chromophores display Verdet constants an order of magnitude higher than commercial inorganic Faraday rotators. Critical to the development of new generations of organic materials is the ability to organize them in optimal structures for optical coupling/measurements. We report herein the synthesis of a dodecyl-substituted hexapyrrolohexaazacoronene (C12-HPHAC) displaying discotic liquid crystalline (LC) properties and large Faraday rotation. Thin films with a redox mixed C12-HPHAC/C12-HPHAC+2 composition display a discotic columnar LC phase, are stable to air and moisture in the solid and solution states, and achieve a maximum Verdet constant of 3.36 × 105 deg T-1 m-1 at 700 nm. This result is consistent with Serber's model of magnetic circular birefringence and displays one of the largest reported Verdet constants for organic materials in the UV-Vis range. The LC phase aligns the molecules and leads to gains in Verdet constants of up to 105% through the favorable orientation of the molecules' magnetic and electric transition dipole moments with respect to the applied magnetic field.

Hetero-Bimetallic Ferrocene-Containing Zinc(II)-Terpyridyl-Based Metallomesogen: Structural and Electrochemical Characterization.

The synthesis, as well as the mesomorphic and electrochemical properties, of a hetero-bimetallic coordination complex able to self-assemble into a columnar liquid crystalline phase is reported herein. The mesomorphic properties were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and Powder X-ray diffraction (PXRD) analysis. Electrochemical properties were explored by cyclic voltammetry (CV), relating the hetero-bimetallic complex behaviour to previously reported analogous monometallic Zn(II) compounds. The obtained results highlight how the presence of the second metal centre and the supramolecular arrangement in the condensed state pilot the function and properties of the new hetero-bimetallic Zn/Fe coordination complex.

A novel strategy for constructing fluorescent liquid crystals with diphenylacrylonitrile groups derivatives based on Thiazolo[5,4-d]thiazole core

In this work, we reported a new series of multifunctional molecular columnar liquid crystalline phases with different terminal functional groups, MTM-1, MTM-2 and MTM-3. The macromolecule materials exhibited an ordered hexagonal columnar mesophase, high thermal stability, and excellent AIE properties in the THF-H2O system. Furthermore, it has been demonstrated that changing the terminal electronic affects the intermolecular forces and thus has a significant effect on the temperature range of the columnar mesophase. Specifically, the fluorescence quantum yield of MTM-1 in the solid state is as high as 45%. It is worth highlighting that the peripheral electron supply effect is favorable to enhance the fluorescence quantum yield. This work provides a new method for designing and synthesizing novel AIE liquid crystal materials.

Benzo[1,2-b:4,3-b’]dithiophene-pyridine isomers: Synthesis, self-assembly, photophysical and acidochromic properties

Two benzo[1,2-b:4,3-b’]dithiophene-pyridine-based bent shaped isomers (3BDTPy12 and 4BDTPy12) have been synthesized via Suzuki coupling reactions as key steps. They differ themselves in the position of N-atom on the pyridine unit which has generated significant effect on their self-assembly behavior and photophysical properties. 4BDTPy12 with N in the para position in the pyridine ring can self-assemble into a columnar liquid crystalline phase while its isomer 3BDTPy12 with N in the meta position in the pyridine ring is only a crystal. Both compounds can form gels in different organic solvents but with different morphologies. The influence of the solvent polarities and doping agents including chiral L-phenylalanine (L-Phe), trifluoroacetic acid as well as L-tartaric acid on their gel morphologies were also studied. The gel of 4BDTPy12 doped with L-tartaric acid could produce enhanced yellow emission which can be used to generate WLED, and such compounds can be used as chemosensors towards volatile acid-base vapors with good reversibility.

Semi-flexible star-shaped molecules: conformational analysis of nano-segregated mesogens forming columnar liquid-crystal phases

Abstract The structural prerequisites are investigated, which make star-shaped molecules suitable precursors for the formation of columnar liquid-crystalline phases. Electronic structure calculations on smaller mesogens show that not all conformers exhibit the atomistic structure, the stability against distortion, and additional dipole moments, which favour columnar stacking. For the presently studied compounds with short terminating alkyl chains, the calculations indicate that the steric factor becomes dominant with increasing star size. Thus, the optimised geometric structures were employed to generate a simplified mathematical model of the structures, which accounts only for the steric interaction in the larger stars. With the help of these diagrams, the most common conformers of star-shaped molecules can be derived in a systematic fashion.

Synthesis and liquid crystalline behavior of hydrazide-functionalized triphenylenedicarboxyimides

ABSTRACT Seven hydrazide-functionalised triphenylenedicarboxyimides (TDIs) which contain a benzamide group bearing different polar substitutes connected to the imide N atom have been studied with the aim to establish the effect of hydrogen bonding and polar substituents on their mesomorphism properties. Six of seven hydrazides each form two types of hexagonal columnar liquid crystalline (LC) phase, including a low-temperature Colho phase and a high-temperature Colhd phase, which were confirmed by characteristic pseudo focal conic fan-shaped textures and XRD measurements. Temperature-dependent FT-IR studies indicated that hydrogen bonding is not strong enough to exist in the LC phases of these hydrazides and disfavours the stabilisation of the columnar mesophase. Nevertheless, dipole–dipole effects were found to favour the mesophase stabilities of these compounds, and the position of the lateral substituent attached to the end benzene ring has a significant impact on the self-assembly by affecting the overall dipole moment.

Ordered hexagonal columnar liquid crystalline self-assembly of mesogen-free sulfonylated side-chain chiral polyethers and their high dielectric property

To achieve large spontaneous polarization for ferroelectric liquid crystalline polymers, we have designed a series of mesogen-free isotactic polyethers with sulfonylated side chains. Different from prior studies using linear alkyl side chains, in this work a methyl branch was implemented in the alkyl side chains of the chiral polyethers. As a result of the continuous twist from the methyl branches and strong dipole-dipole interactions among neighboring sulfonyl groups, a helical chain conformation with tilted side chains was achieved. When the branched side chains were short (e.g., C5) and double chirality existed in both the main chain and side chains, a crystalline structure was obtained. When the branched side chains were long (e.g., ≥ C8) and single chirality existed in the main chain, an ordered hexagonal columnar liquid crystalline phase was induced. Their high-field dielectric property was studied by electric displacement-electric field (D-E) loop tests; however, no ferroelectric behavior was observed up to 200 MV/m. It was considered that the dipole-dipole interaction among neighboring sulfonyl groups in the helical chains was too strong to allow easy ferroelectric flipping.

Unveiling the Role of Hydrogen Bonds in Luminescent N-Annulated Perylene Liquid Crystals.

We report the liquid‐crystalline (LC) and luminescent properties of a series of N‐annulated perylenes (1–4) in whose molecular structures amide and ester groups alternate. We found that the LC properties of these compounds not only depend on the number of hydrogen‐bonding units, but also on the relative position of the amide linkers in the molecule. The absence of amide groups in compound 1 leads to no LC properties, whereas four amide groups induce the formation of a wide temperature range columnar hexagonal phase in compound 4. Remarkably, compound 3, with two amide groups in the inner part of the structure, stabilizes the columnar LC phases better than its structural isomer 2, with the amide groups in the outer part of the molecule. Similarly, we found that only compounds 1 and 2, which have no hydrogen bonding units in the inner part of the molecule, exhibit luminescence vapochromism upon exposure to organic solvent vapors.

Columnar Liquid Crystalline Corannulenes: Synthesis, Assembly and Charge‐Carrier Transport Properties

Main observation and conclusionTwo discotic liquid crystalline (LC) molecules consisting of a bowl‐shaped corannulene core and five‐fold photoactive azobenzene branches with different paraffinic side chains were developed. Their self‐assembly, photo‐responsive behavior and charge‐carrier transport properties were investigated in detail. A wider mesophase temperature range was achieved when utilizing longer and furcal flexible side chain substitution. 2D XRD measurements revealed the π‐packed corannulene‐centered 1b (i.e., with furcal side alkoxyl chains) exhibited helical columnar LC phase. This packing structure also led to a higher hole charge carrier mobility of 7.07 x 10–2 cm2·V–1·s–1 compared to that of the counterpart 1a with linear side chain substitutions.

Liquid-crystalline 1,4-benzoquinone derivative: Self-assembling behavior and redox properties

1,4-Benzoquinone has an important structural motif and target to develop compounds for pharmacology, organic electronic, and natural products. Herein, we synthesized and characterized a series of benzoquinone derivatives BQ, BQ2, and BQ4. Cyclic voltammetry showed that BQ2 and BQ4 have both electron-accepting and electron-donating properties. X-ray diffraction, polarized optical microscopic observations, and DSC measurement indicated that BQ4 self-assembled into the hexagonal columnar liquid-crystalline (LC) phase in the wide temperature range including room temperature, whereas BQ2 was crystal. We carried out the single crystal X-ray analysis of BQ to investigate the molecular arrangement of benzoquinone cores in the column LC phase of BQ4, in which each benzoquinone core was isolated by surrounding of four phenyl moieties not to interact with each other. Also, BQ was nonpolar evaluated by density functional theory (DFT) calculations. As a result, propeller-like BQ4 molecules stack into the column structures dependent on molecular shape.

Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT‐Derived Polycatenar Molecules

AbstractFirst examples of multichain (polycatenar) compounds, based on the π‐conjugated [1]benzothieno[3,2‐b]benzothiophene unit are designed, synthesized, and their soft self‐assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan‐shaped 2‐brominated 3,4,5‐trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non‐dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase.

Photo-electrical response of nanocomposites from single-walled carbon nanotubes incorporated in tris(keto-hydrozone) discotic mesogen

We report an experimental study on photo-electrical response of new nanocomposites produced from discotic mesogen LTTH-6 (possessing columnar liquid-crystalline phase) and single-walled carbon nanotubes (SWCNTs) with diameter ∼ 1.5 nm. The SWCNTs were incorporated in LTTH-6 at concentration of 1 wt.%. Thin layers of SWCNTs/LTTH-6 nanocomposites were formed with a thickness of 3 μm. The light-induced change in electrical conductivity of these layers was ascertained at room temperature by current-voltage measurements, upon illumination with a low-intensity (∼ 1 mW/cm2) continuous visible light. The effect of photoresponsivity of the glassy-like columnar phase of SWCNTs/LTTH-6 manifests the potential of such nanocomposites to be functional materials for applications in molecular electronics, sensorics and mechatronics.

A structural parameter to link molecular geometry to macroscopic orientation in discotic liquid crystals: study of metalloporphyrin tapes

Novel liquid crystalline (LC) molecules were prepared from a dimeric porphyrin tape. A series of metal complexes (1Zn, 1Pd, 1Cu, and 1Ni) and the free-base form (12H) of the porphyrin tape formed a columnar LC phase. Although only the central metal ions were different among these compounds, 1Ni, 12H, and 1Cu aligned homeotropically in a sandwiched glass cell, while 1Zn and 1Pd exhibited a random orientation at a macroscopic scale. The strength of the π-π interactions, tunable by the distortion of the porphyrin cores through metallation, is a key factor for the observed macroscopic orientation difference.

Dipyrrolyldiketonato Titanium(IV) Complexes from Monomeric to Multinuclear Architectures: Synthesis, Stability, and Liquid-Crystal Properties.

Dipyrrolyldiketone ligands (dpkH) are used with Ti(OiPr)4 to afford monomeric titanium(IV) complexes displaying the general formula C2-[Ti(dpk)2(OiPr)2]. The dpkH ligands employed consist of two dipyrrolyldiketone compounds (2H and 3H) and three diphenyl-substituted analogues (4H-6H). The behavior of these octahedral [Ti(dpk)2(OiPr)2] species in solution was investigated by 1H NMR at variable temperatures. Dynamic phenomena were evidenced, and the activation parameters associated with these processes (ΔH⧧, ΔS⧧, and ΔG⧧) were retrieved. [Ti(dpk)2(OiPr)2] complexes are precursors for the formation of high-nuclearity aggregates whose structures depend on the substituents on the diketone backbone. The crystal structures of monomeric ([Ti(1)2(OiPr)2]; 1 is the 1,3-diphenyl-1,3-propanedionato ligand) and [Ti(2)2(OEt)2]), dimeric ([Ti2(1)4(μ2-O)2]), and tetrameric ([Ti4(4)8(μ2-O)4]) species have been established, and the origin of this structural diversity is discussed. The solid-state optical properties of several complexes were determined and interpreted with the help of DFT calculations. Finally, the dinuclear complex [Ti(6)2(μ2-O)2] was synthesized, where ligand 6 incorporates six long alkyl chains (C16H33). This complex shows rich mesomorphic properties, with an original room-temperature plastic crystal phase followed by a hexagonal columnar liquid-crystalline phase.

Corrosion inhibitor by a polymerizable columnar mesogen based on hexabenzocoronene derivative

AbstractA hexa‐peri‐hexabenzocoronene derivative (HBC‐1,2,4‐Ph‐DA‐C12) with the central HBC core tethered with three diacetylene (DA)‐containing chains and three saturated alkyl chains was applied for the anticorrosion of an iron surface. This compound, which exhibits a columnar liquid crystalline phase, could be polymerized by ultraviolet irradiation through reactions between the DA units. This polymer coating exhibited a good anticorrosion property with good hydrophobicity (contact angle [CA] ~ 84°–105°) and excellent mechanical property. It showed a high resistance of 149 kΩ/cm2, much higher than that of known anticorrosion materials.